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Report FILE ciP a n ,_ i _ 1 _ ,,,--, s ,I . _-, Z. r, C ', 2 • Seismic S Hazard Invest Alberta Rider Elementary School Tigard- Tualat School Distr 23J Tigard, Oregon URS Job # 25695391.10001 ter. pr .' j 4 :, , A,. 2 6+A� fl is _ _ �_ � '"' fi , 'f'.2" r - '`°8 yes ■ ,{ 1 ... . l 0 nTryTT" ?' a e , :yam. Prepared for Tigard- Tualatin School i!..H ut 23J 13u 17z.o a ct-0 06 !I gt Jul 2003 July R 114 q 0 0 0 Prepared by URS Corporat URI; I URADS a July 31, 2003 1. 1 Tigard- Tualatin School District 23J 6960 SW Sandburg Street I Tigard, Oregon 97223 Attn: Mr. Stephen Poage 1 Director of Capital Projects Re: Seismic Site Hazard Investigation I Alberta Rider Elementary School Tigard- Tualatin School District 23J I Tigard, Oregon URS Job No: 25695391.10001 $ Dear Mr. Poage: We are pleased to submit herewith our report entitled "Seismic Site Hazard Investigation, I Alberta Rider Elementary School, Tigard - Tualatin School District 23J, Tigard, Oregon." This report formally documents our conclusions and recommendations regarding the proposed project. I It has been our pleasure to assist you with this project. Should you have any questions regarding the contents of this report, please call us at your convenience. Yours very truly, I URS Corporation I � 4: -14 -, ■ :V :i . * �OF 1 0 CbIl7" - S ,l _ 17/ OR I Bryan J. Duevel, PE r ne�' 7. JO Q .� Bnan M. Willman, Ph.D., P.E. Project Engineer Manager Geotechnical Engineering EXPIRES: _1(7 '' t ,1 URS Corporation 111 SW Columbia, Suite 900 Portland, OR 97201 -5814 Tel: 503.222.7200 Fax: 503.222.4292 I TABLE OF CONTENTS I Section 1 Introduction 1-1 1.1 General 1 -1 1.2 Scope of Work 1 -1 Section 2 Geologic Setting 2 - 1 I i 2.1 Site Description 2 -1 2.2 Regional Geologic Structure 2 -1 2.3 Site Geology 2 -1 2.4 Site Hydrogeology 2 -2 1 Section 3 Seismic Conditions 3 -1 3.1 Earthquake Effects - General 3 -1 1 3.2 Historical Seismicity 3 -1 3.2.1 Significant Earthquakes 3 -1 3.2.2 Summary 3 -3 I 3.3 Earthquake Sources 3 -3 3 -4 Fault Descriptions 3 -4 3.4.1 Helvetia Fault Zone 3 -5 1 3.4.2 Newberg Fault 3 -5 3.4.3 Portland Hills Fault 3 -5 3.4.4 Bolton Fault 3 -6 1 3.4.5 Mt. Angel Fault East Bank Fault 3 -7 3.4.7 Oatfield Fault 3 -7 3.4.8 Clackamas River Fault Zone 3 -7 3.4.9 Grant Butte, Damascus, Tickle Creek Fault Zone 3 -8 3.4.10 Other Fault Zones 3 -8 3.4.10.1 Sherwood Fault 3 -8 3.4.10.2 Dairy Creek Fault 3 -8 i; 3.4.10.3 Beaverton Fault 3 -9 3.4.11 Cascadia Subduction Zone 3 -9 3.4.11.1 Megathrust 3 -9 1 Section 4 Design Ground Motion 4 - 1 4.1 Ground Motion Analyses 4 -1 I , 4.1.1 Geomatrix 1995 Probabilistic Study 4 -1 4.1.2 URS 2001 Probabilistic Study 4 -1 I 4.1.3 URS/DOGAMI 2000 Portland Metropolitan Study 4 -1 4.1.4 1998 OSSC Zonation 4 -1 4.1.5 Results Comparison 4 -2 4.2 Recommended Design Ground Motions 4 -2 URS \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 i 1 TABLE OF CONTENTS 1 Section 5 Seismic Hazard Evaluation 5-1 I 5.1 Anticipated Foundation Design 5 -1 5.2 Seismic Hazards 5 -1 5.2.1 Liquefaction Hazard 5 -1 5.2.2 Tsunami /Seiche Hazard 5 -1 5.2.3 Seismic Slope Stability Hazard 5 -1 5.2.4 Surface Rupture Hazard • 5 -2 5.2.5 Ground Shaking Amplification Hazard 5 -2 ill Section 6 Closure 6 -1 • 1 Section 7 References 7 -1 List of Tables Table 1 Comparison of Peak Ground Accelerations 4 -2 List of Figures I I 1 Figure 1 Vicinity Map Figure 2 Site Map 1 Figure 3 Tectonic Structures f the Tualatin Basin 1 I I I . I . I S \\Por6\projects\25695391 TTSD Alberta Rider` TTSD _seisrrnc_hazard.doc\31- JUL -03 ii SECTIONONE Introduction 1.1 GENERAL This report presents the results of our seismic site hazard investigation for the proposed Alberta Rider Elementary School in Tigard, Oregon. This work was completed in accordance with our proposal to Tigard- Tualatin School District 23J dated May 16, 2003. The project site is located approximately as shown on the Vicinity Map, Figure 1. The project involves the construction of a new elementary school with a footprint of approximately 40,000 square feet, as well as an entrance drive, parking lots and play fields. The Site Map presented on Figure 2 shows a preliminary plan layout of the site. The proposed school is considered to be a "special occupancy structure" under Oregon Revised Statutes (ORS) 455.447. As such, a seismic site hazard investigation is required per Oregon Structural Specialty Code (OSSC) Section 1804.1. This report is prepared in accordance with OSSC Section 1804.3.2. The purpose of this report was to evaluate the surface and subsurface conditions at the site and to evaluate the potential seismic hazards of the proposed school. This report is a companion to the geotechnical report entitled "Foundation Investigation, Alberta Rider Elementary School, Tigard- Tualatin School District, Tigard, Oregon." This report was submitted to the Tigard- Tualatin School District in July 2003. 1.2 SCOPE OF WORK The scope of this investigation included completion of the following: 1. Description of the site geologic setting including regional geology, site topography, subsurface stratigraphy and groundwater. 2. Description of the seismic setting including the regional tectonic framework, historical seismicity, and potential earthquake sources. 3. Probabalistic and deterministic analyses to assess design earthquake ground motions. 4. Evaluation of seismic hazards including landslides, liquefaction, regional subsidence /collapse, fault surface rupture, and tsunami /seiche inundation. 5. Preparation of five copies of this report describing the results of this investigation. URS I \\Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc131- JUL -03 1 -1 I SECTIONTWO Geologic Selling 1 I 2.1 SITE DESCRIPTION The site is located near the crest of Bull Mountain as shown on the Vicinity Map, Figure 1. The I topography across most of the site is relatively gentle, with elevations ranging from a high of approximately 574 feet above Mean Sea Level (MSL) along the northwestern boundary to the • site to 515 feet above MSL in the far southeast corner of the site. The maximum slopes present I onsite approach 25% at the northwest edge of the site. Elsewhere, maximum slopes are approximately 15 %, located in the northwest and southeast portions of the site 1 2.2 REGIONAL GEOLOGIC STRUCTURE The site is located in the northern Willamette Valley physiographic province, an elongate, I roughly north -south trending alluvial valley that lies between the Coastal Range and Cascade Mountains to the west and east, respectively. Marine sedimentary rocks and basalt are found below the alluvial sediments (On, et. al., 1992). The Northern Willamette Valley has undergone I substantial structural deformation since the Eocene, resulting in the Portland fold belt as defined by Unruh et al. (1994). The tectonic underpinnings of the Portland Fold Belt are not well understood and complicated by the fact that this area lies in a transition zone between the rotating I i forearc block and the continental interior (Wells et al, 1998). Specifically, the project site is located in the Tualatin Basin, a northwest trending synclinal I subbasin to the Willamette Valley basin (Unruh et al., 1994). The Tualatin Basin is fault bound by structurally controlled, northwest- trending highlands, specifically along its northeastern margin by the Portland Hills and on the southwestern edge by the Chehalem Mountians (Madin, I 1990). The two highlands are parallel to mapped regional faults including the East Bank fault, the Portland Hills fault, the Oatfield fault, the Mollala -Canby fault, the Gales Creek fault, the Newberg fault, and the Mt. Angel fault. I Internal structure to the basin includes the faulting that has resulted in the formation of the Bull Mountain and Cooper Mountain anticlines. The site is located immediately south of the anticline I axis as mapped by Madin. . 2.3 SITE GEOLOGY 1 Subsurface investigation of the site was performed in June 2003. The investigation was comprised of 15 test pits and 3 soil /rock core borings. The locations of these explorations is 1 shown in Figure 2. The site is underlain by approximately 5 to 9 feet of medium stiff brown clay. This clay is weathered late Quaternary windblown silt. Underlying the weathered silts is 2 to 6 feet of stiff reddish brown lean clay. This clay is basalt bedrock residuum that grades to extremely to highly weathered basalt at depths ranging from 8 to 16 feet below ground surface. The basalt bedrock is Miocene -aged Columbia River Basalts. The highly weathered basalt is very weak (indicating it I , can be pealed with a pocketknife) and highly fractured. The degree of weathering gradually decreases with depth. The rock grades to moderately weathered, moderately strong (requiring a I hammer blow to break a sample) basalt at depths between 21 and 26 feet bgs. 1 \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seisrruc_hazard.doc131- JUL -03 2 -1 I I SECTIONTWO Geologic Setting i 2.4 SITE HYDROGEOLOGY I Groundwater was not encountered during the subsurface investigation. URS conducted a review of water well logs publicly available from the Oregon Water Resources Department. Static groundwater levels reported on well logs are in excess of 150 feet bgs in the vicinity of the site. Perched groundwater may be present within the fine - grained soils during the winter months. However, discharge from these perched systems is anticipated to be minimal. I II 1- 1 I 1 I I I 1 r 1 , URS \ \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 2 -2 .1 I SECTIONTHREE Seismic Conditions 3.1 EARTHQUAKE EFFECTS - GENERAL Several factors control the level and character of earthquake ground shaking at a site. Generally, these factors are: (1) rupture dimensions, geometry, and orientation of the causative fault; (2) distance from the causative fault; (3) magnitude of the earthquake; (4) the rate of attenuation of the seismic waves along the propagation path from the source to site; and (5) site factors including the effects of near - surface geology particularly from soils and unconsolidated sediments. Other factors, which vary in their significance depending on specific conditions, include slip distribution along the fault, rupture process, footwall /hanging -wall effects, and the effects of crustal structures such as basins. 3.2 HISTORICAL SEISMICITY Historically, the Portland region has been characterized by a moderate level of seismicity with the largest earthquakes not exceeding magnitude (M) 6 (Bott and Wong, 1993). A historical earthquake catalog of all known events in northwestern Oregon and southwestern Washington for the period 1841 to 2000 was compiled. Earthquake data were acquired from: a catalog compiled by Woodward -Clyde Consultants (URS) for DOE Hanford; Ludwin (1991); University of Washington; National Earthquake Information Center; Stover, Reagor and Algermissen; the Decade of North American Geology; and the Council of the National Seismic System earthquake catalog. This catalog contains over 18,000 events, a large percentage of which are associated with the St. Helens seismic zone. Only 5 earthquakes are M 6.0 or larger and these all occurred at distances greater than 80 km from the proposed school site. Approximately 38 earthquakes in the • catalog have magnitudes between M 5.0 to 5.9, the largest of which is the 1993 moment magnitude (Mw) 5.6 Scotts Mills earthquake. In characterizing earthquake occurrence, historical earthquakes can generally be divided into pre- instrumental and instrumental periods. Prior to adequate seismographic coverage, the detection of earthquakes was generally based on direct observation and felt reports. Thus results are strongly dependent on population density and distribution. This part of the Pacific Northwest is typical of much of the western United States, and was sparsely populated in the 1800's. Therefore the detection of pre - instrumental earthquakes shows varying degrees of completeness. The pre- instrumental historical record is estimated to be complete for earthquakes of Richter local magnitude (ML) 5 and larger since about 1850 for the Portland region. Seismograph stations were established in 1906 in Seattle and 1944 in Corvallis, but adequate seismographic coverage of 1 small events (M < 3.0) did not begin in northwest Oregon until about 1980 when the University of Washington expanded its regional network. The historical record is complete for M 2.5 and greater only since 1980 (Bott and Wong, 1993). 3.2.1 Significant Earthquakes Significant earthquakes and earthquakes greater than M 6.0 in the region are discussed below. Earthquakes are described with the modified Mercalli intensity (MMI) that rates intensity from I (lowest — generally not felt) to XII (highest — total damage) (Kramer, 1996). URS \\Por6\protects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 3 -1 I SECTIONTHREE Seismic Conditions 1 1872 North Cascades Earthquake I On 15 December 1872, a large earthquake occurred in the wilderness of central Washington with an approximate ML 7.4 (Malone and Bor, 1979). The exact source of the earthquake is unknown. i The event generated an approximate intensity of MM IV -V in the region of the proposed school (Woodward -Clyde Consultants, 1992). I 1873 Crescent City Earthquake On 23 November 1973 an earthquake of estimated MW 7.3 (Bakun, 2000) occurred near the ;1 Oregon- California border east - southeast of Brookings, though there are large uncertainties as to its exact location. This earthquake may be a rare example of an intraslab event in western Oregon (Ludwin et al, 1991; Wong, 1997). The event had a maximum intensity of MM VIII, and an : 11 intensity of MM III -IV in the region of the proposed school (Toppozada et al., 1981). 1 1877 Portland Earthquake .The earliest known historical earthquake in the Portland region occurred on 12 October 1877. Two events were actually reported on this day, one which probably occurred near Cascades, I, Washington and had a maximum intensity of MM III. The other event occurred near Portland and had a maximum intensity of MM VII. The larger of the two events, it has an estimated magnitude of ML 51/4 (Bott and Wong, 1993). At the Alberta Rider Elementary site, the intensity was estimated to be MM IV (Bott and Wong, 1993). 1939 Southern Puget Sound Earthquake On 13 November 1939, an earthquake of surface wave magnitude (Ms) 5 occurred in southern Puget Sound. It had a maximum intensity of MM VII and an intensity of MM IV in the region of the school site (Stover and Coffman, 1993). I 1949 Puget Lowland Earthquake • On 13 April 1949, the largest historic event in the Puget Sound region occurred northeast of Olympia, Washington, with a body wave magnitude (m of 7.1. The event occurred at a depth i of 54 km within the Juan de Fuca plate. Eight people were killed, many injured and property damage was sustained at a loss of $25 million. The intensity in the region of the school site was II MM VI -VII (Thorsen, 1986). 1962 Portland Earthquake I . On 6 November 1962, an earthquake occurred 15 km northeast of downtown Portland with a ✓ magnitude of ML 5.2 to 5.5, a depth of 16 km, and a maximum intensity of MM VII. This I earthquake was felt throughout northwest Oregon and southwest Washington. The intensity in the region of the school was MM V -VI (Wong and Bott 1995). This is the second largest earthquake known to have originated in the Portland region (Bott and Wong, 1993). I \ \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seisrruc_hazard.doc131- JUL -03 3-2 I I SECTIONTHREE Seismic Conditions 1965 Puget Lowland Earthquake On 29 April 1965, the second largest known event to date in the southern Puget Sound occurred • north of Tacoma with a mb 6.5. The event, an intraslab earthquake, occurred at a focal depth of 60 km and was widely felt. Six people were killed and damage reached an estimated $12.5 million. The earthquake had a maximum intensity of MM VIII and a probable intensity of MM • V in the vicinity of the proposed school (Thorsen, 1986). 1981 Elk Lake Earthquake On 14 February 1981, the largest known earthquake associated with the St. Helens seismic zone occurred with a mb 5.1. The aftershock zone delineates a fault zone 5 to 12 km in depth. The maximum intensity of MM VI was reported for the epicentral region and an intensity of MM V for the school vicinity (Bott and Wong, 1993). 1993 Scotts Mills Earthquake 1 On 25 March 1993, an earthquake occurred near Scotts Mills in western Oregon with a q g magnitude of M 5.6, a depth of 16 km, maximum intensity of MM VII, and an intensity MM V- VII in the school vicinity. It caused over $28 million in property damage. This earthquake is thought to have occurred on the Mount Angel fault. Through 1994, over 300 aftershocks had been recorded (Thomas et al., 1996). 2001 Nisqually Earthquake 1 On 28. February 2001 at 18:54 GMT, an earthquake occurred approximately 17 km northeast of Olympia, Washington. The earthquake had a magnitude of M, 6.8 at a depth of 52.4 km. Damage from the earthquake was widely reported throughout the Seattle and Olympia areas. The earthquake had a maximum intensity of MM III -IV in the vicinity of the new school (University • of Washington). 3.2.2 Summary The strongest ground shaking that the area of the proposed school has historically experienced appears to be MM VI -VII in the 1949 earthquake and MM V -VII in the 1993 Scotts Mills event. A MM VII intensity is roughly equivalent to a peak horizontal acceleration of 0.18 to 0.34g (Wald et al., 1999). 3.3 EARTHQUAKE SOURCES The Pacific Northwest has four types of seismic sources due to the presence of the Cascadia subduction zone. These sources include (1) the subduction zone megathrust, which represents the boundary (interface) between the downgoing Juan de Fuca plate and the overriding North American plate; (2) faults located within the Juan de Fuca plate (referred to as the intraplate or intraslab region); (3) crustal faults principally in the North American plate; and (4) volcanic 1 sources beneath the Cascade Range (Wong and Silva, 1998). URS \Por6\prajects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 3-3 I ii SECTIONTHREE Seismic Conditions In the past two decades, significant geologic, seismologic, and geophysical studies have been I undertaken to investigate seismic sources in the Pacific Northwest. Such studies, particularly along the coast of the Pacific Northwest, have been the key to our understanding of the I earthquake processes within the Cascadia subduction zone. Few paleoseismic studies to investigate crustal faults, however, have been performed west of the Cascades because of dense vegetation, relatively rapid erosion rates, and past glaciation, which makes it difficult to find evidence of young faulting (e.g., Pezzopane, 1993). Alternative approaches such as subsurface imaging are now being carried out in the Portland area (e.g., Blakely et al., 1995) and the Puget Sound region .(e.g., Johnson et al., 1999). I In the following section, we identify and characterize the seismic sources that are significant to seismic hazards near the school. As specified in OSSC 1804.2.1.1, the probable source faults must all be individually examined for contribution to site hazards. For this analysis, the I earthquakes need to be defined for each seismic source considered in the seismic hazard assessments by their the Maximum Credible Earthquake (MCE). The MCE is commonly defined as "the largest earthquake that is capable of being produced from a source, structure, or region, I under the currently known tectonic framework. It is a rational and believable event that can be supported by all known geologic and seismologic data. An MCE is determined by judgment considering the geologic evidence of past movement and the recorded seismic history of the ,' area." We adopt this definition in these assessments. 3.4 FAULT DESCRIPTIONS I Because of their roximit crustal faults are possibly the most significant seismic sources to P Y� P Y tm I inland sites. Studies by Pezzopane (1993) and Geomatrix Consultants (1995) show that at least 70 crustal faults that may have earthquake potential exist in Oregon. Many of these faults were unknown or not recognized as being seismogenic a decade ago. Although the largest known II crustal earthquake in western Oregon is only about Mw 6 (Wong and Bott, 1995), potential exists . for events of Mw 61/2 or greater along several recognized faults including the Portland Hills and the recently discovered East Bank faults in Portland and the Gales Creek -Mt. Angel fault zone I (Wong et al., 1999). As discussed earlier, the Mt. Angel fault is the possible source of the 1993 Scotts Mills Mw 5.6 earthquake. Several crustal faults occur in the vicinity of the proposed school site that are either active or il potentially active. There has not been a historic surface rupture earthquake on any fault within northwest Oregon and, to date, paleoseismic investigations of the regional faults has been limited. However, historical seismicity in the region appears, in a few cases, to be associated with I mapped faults. In addition, some regional seismotectonic studies have been conducted that provide preliminary data regarding the potential activity of these faults. I The major fault features that have an effect on seismic hazards within the Tualatin basin as identified in the Unruh et al (1994) report are the Portland Hills Fault Zone (which includes the East Bank and Oatfield Faults), the Newberg Fault, the Grant Butte Fault, and the Bolton Fault. I These features are shown on Figure 3. Several fault features that should be considered in a seismic hazard assessment, but are not labeled on the Unruh et al (1994) map include the Clackamas River Fault Zone and the Helvetia Fault. I \ \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 3-4 I • I SECTIONTHREE Seismic Conditions Seismic source characterization is concerned with three fundamental elements: (1) the identification of significant sources of earthquakes; (2) the maximum size of these earthquakes; and (3) the rate at which they occur. The faults described below all could potentially effect the new school site. All faults are dominantly lateral -slip faults and are assumed to extend to the full extent of the seismogenic crust (approximately 15 to 25 km; Wong, 1997). Maximum earthquake magnitudes were estimated based on the empirical relationship of Wells and Coppersmith (1994) between moment magnitude (M and surface rupture lengths for all types of faults. Length estimates were taken from mapped fault lengths. 3.4.1 Helvetia Fault Zone • The north- northwest - striking Helvetia fault is located about 21.6 km from the proposed school. The fault is about 10 km as measured in the subsurface, and is identified from seismic reflection !. images and water well logs. The fault possibly displaces overlying Miocene - Pliocene to Pleistocene sediments down -to- the -west by as much as 20 m (Yeats et al., 1991). The Helvetia fault is not exposed at the surface, however, based on a lack of evidence disputing the activity of the fault. Geomatrix Consultants (1995) considered the fault to be potentially active. 3 3.4.2 Newberg Fault The Newberg fault trends northwest and has a subsurface length of about 8 km. The fault is ' located approximately 17 km to the southwest of the proposed school. The fault displaces the top of Columbia River Basalt by about 250 meters down -to- the - southwest. Anomalous aeromagnetic and gravity gradients also indicate the presence of the fault (Geomatrix Consultants, 1995; Yeats et al., 1991). Silvio Pezzopane (U.S. Geological Survey) documented lineaments in fluvial terraces and bedrock notches along the projection of the Newberg fault (Geomatrix Consultants, 1995). No seismicity is recorded along the trend of the Newberg fault, and although there is no direct evidence for activity of the Newberg fault, the along -strike proximity of the fault to the seismically- active Mt. Angel fault suggests that it may be potentially active. Although the maximum measured subsurface length of the fault is 8 km, we consider the fault to have a longer potential surface rupture of 17 km. This length is based on a minimum magnitude of M 6.5 that appears to be necessary to produce surface rupture in western Oregon. 3.4.3 Portland Hills Fault The Portland Hills fault zone includes a series of northwest- trending subsurface faults that extend for a distance of about 40 km along the eastern margin of the Portland Hills ( Geomatrix Consultants, 1995; Madin, 1990). Extension of the fault toward the southeast, beyond the Portland Hills, based on aeromagnetic gravity (Blakely et al., 1995) and high- resolution seismic reflection imaging (Pratt et al., 2001), provides a total estimated fault length of about 62 km. The closest approach of the Portland Hills fault to the proposed school site is approximately 13.2 km. Several interpretations have been proposed to describe the style of faulting and the kinematic setting of the Portland Hills fault. Based on the interpretation of surface geology, geomorphology, gravity data, and seismicity, Beeson et al. (1985; 1989) have described the Portland Hills fault as a structurally complex dextral strike slip zone with minor normal faulting. \\Por6\projects\25695391 TTSD Alberta RiderI TTSD _seisrruc_hazard.doc131- JUL -03 3-5 I SECTIONTHREE Seismic Conditions Yelin and Patton (1991) consider the Portland Hills fault to be an active right- lateral strike -slip 1 fault within an en echelon, releasing step of a large dextral slip zone. In contrast, the Portland Hills are thought by some researchers (Beeson et al., 1989; Unruh et al., 1994) to be the surface expression of an anticline associated with the hanging wall of a southwest - dipping thrust fault. The age of the most recent event along the Portland Hills fault is not clearly understood. Recent investigation of the southern Portland Hills fault using high - resolution seismic reflection I methods, provides evidence for faulting of Missoula flood deposits. The flood sediments are faulted at least several meters down -to- the -east along the fault. Although no direct estimates for the age of the sediments are available, the most recent catastrophic floods in the area occurred ' about 15.5 to 13 ka (Madin, 1990). This suggests that the Portland Hills fault has been active in about the past 13 ka. A swarm of M < 3.5 earthquakes occurred at the northern end of the Portland Hills fault in 1991 (Blakely et al., 1995). Focal mechanisms from the largest event suggest a mixed right - lateral and reverse mechanism for the fault (Blakely et al., 1995). Based on a maximum estimated length of 62 km (Wong et al., 2000), which includes projection of the fault to the south of the Portland Hills, an estimated MCE of M 7.2 is calculated for the Portland Hills fault. 3.4.4 Bolton Fault The Bolton fault appears at the surface as a 9-km-long northwest - striking structure located PP g b between the northern Willamette Valley and the Portland Basin. At its closest approach the fault is about 9.6 km from the proposed school site. Beeson et al. (1989) map the fault as a high- angle, down -to- the - northeast structure that displaces late Pleistocene (11 to 14 ka) flood deposits. Unruh et al. (1994) were unable to confirm displacement in stream exposures of Miocene Columbia River Basalts or Plio- Pleistocene conglomerates. Instead, they suggest that scarps along the fault may be the result of erosion. Unruh et al. (1994) and Geomatrix Consultants (1995) both considered the Bolton fault to be potentially active. Although the maximum mapped surface length of the Bolton fault is 9 km, the estimated minimum magnitude earthquake that we consider sufficiently large to produce surface rupture is Mw 6.5. This MCE corresponds with an associated surface rupture length of 17 km. 3.4.5 Mt. Angel Fault The Mount Angel fault is a 24- to 32 -km -long northwest- trending fault located approximately 25.3 km to the southwest of the proposed school site. The fault strikes northwest and dips . steeply to the northeast. The fault is mapped at the subsurface based on seismic reflection lines, water well logs, and seismicity (Geomatrix Consultants, 1995; Yeats et al., 1991). The top of the Columbia River Basalt group and Mio- Pliocene fluvio- lacustrine deposits are displaced by the fault. In 1993, the MW 5.6 Scotts Mills earthquake occurred about 8 km south of the mapped extent of the Mt. Angel fault (Geomatrix Consultants, 1995). It is still unclear whether the earthquake occurred along the Mt. Angel fault. The focal mechanism for the earthquake suggests that the earthquake involved a northwest - striking fault and suggests subequal right- and reverse slip (Geomatrix Consultants, 1995). Recent investigations along the Mt. Angel fault suggest that faulting has occurred in Missoula flood deposits (Liberty et al., 1996). Recent high - resolution seismic reflection and refraction imaging URS \\Por6\projects\25695391 TTSD Alberta Rider\ITSD _seismic hazard.doc\31- JUL -03 3 -6 I SECTIONTHREE Seismic Conditions I suggests that possible Holocene deposits may also be displaced (Ian Madin, DOGAMI, personal I communication, 2000). Based on potential historic seismicity, displaced Missoula flood deposits, and a surface scarp in Holocene deposits, we consider the Mt. Angel fault to be active. The maximum surface rupture length ascribed to the fault is 32 km (Wong et al., 2000) which I 'corresponds with a MCE of M 6.8. 3.4.6 East Bank Fault I The East Bank fault has been defined based on the P resence of an aeromagnetic signature I (Blakely et al., 1995) and based on high - resolution seismic imaging (Pratt et al., in press). The fault is shown as a magnetic lineament to the northeast and parallel to the Portland Hills fault (Blakely et al., 1995). The fault is believed to be a major structural feature because the I pronounced aeromagnetic anomaly is consistent with vertical displacements of at least 1 km of the basement volcanic rocks (Blakely et al., 1995). The East Bank fault is entirely concealed beneath Quaternary deposits (Madin, 1990). The fault was previously mapped based on an 1 apparent < 200 m vertical offset of the volcanic basement (Blakely et al., 1995). The East Bank fault may serve as a significant component of the eastern margin of the Portland Basin. Pratt et al. (2001) reports that high - resolution seismic imaging indicates that the East Bank fault has had ,, late Pleistocene and possibly Holocene activity. The data suggest that paleochannels of the Willamette River have been faulted, and that the river channel might be fault controlled. Because of the geophysical evidence available for the East Bank fault, we consider the fault to be I active. At its closest projection, the East Bank fault is located about 17.3 km from the school site. The mapped trace of the fault is not well- constrained, however, estimates for the fault length range from 40 to 55 km (Wong et al., 2000), which corresponds with an MCE of Mw 7.1. 1 3.4.7 Oatfield Fault • I The Oatfield fault is recognized on the basis of aeromagnetic anomalies and possible association with historic seismicity (Blakely et al., 1995). The fault is located along the western flank of the Portland Hills and may be structurally associated with the Portland Basin. The school is located I 12.4 km west of the Oatfield fault (Figure 5.9). The fault is mapped by Madin (1990) based on water well data. No definitive surface trace of the fault has been mapped. Blakely et al. (1995) suggest that the northern projection of the Oatfield fault may intersect the 1991 swarm of M < 3.5 I earthquakes that were also considered to be associated with the Portland Hills fault. As with the Portland Hills fault, the style of deformation of the Oatfield fault is not understood. The associated historical seismicity indicates oblique faulting dominated by right- lateral slip with I lesser reverse motion (Blakely et al., 1995). Because of its potential structural and kinematic association with the Portland Hills fault and Portland Basin, and the nearby presence of historical I seismicity, we consider the Oatfield fault to be potentially active. The length of the Oatfield fault is not well- known, but best estimates suggest that it may be up to 40 km long (Wong et al., 2000) which corresponds to an MCE of Mw 6.9. I 3.4.8 Clackamas River Fault Zone I The Clackamas River fault zone includes a series of northwest- trending oblique -slip faults mapped south of Estacada, Oregon along the Clackamas River (Geomatrix Consultants, 1995). \\Por6\prolects\25695391 1TSD Alberta Rider\ TTSD _seisrrnc_hazard.doc\31- JUL -03 3-7 1 I SECTIONTHREE Seismic Conditions The maximum length of faults in the zone is 22 km. Faults within the zone have documented right - lateral and normal displacement (Hammond et al., 1980). The faults displace middle Miocene (ca. 15 Ma) Grande Rhonde and Wanapum Basalts. Late Pliocene to early Pleistocene lavas do not appear to be deformed (Priest et al., 1983; Sherrod and Conrey, 1988). A gravel terrace estimated to be approximately 1 Ma crosses the fault and does not appear to be displaced (Geomatrix Consultants, 1995). Also, no evidence for Quaternary activity was documented during photogeologic analyses for the U.S. Bureau of Reclamation (Geomatrix Consultants, 1995). However, the Clackamas River fault has a similar orientation to the Oak Grove - Lake Harriet fault zone to the south and Geomatrix Consultants suggest that there may be a structural association between the two fault zones. Geomatrix Consultants report that some faults within the Oak Grove - Lake Harriet fault zone may have had Quaternary activity. Because of this possible association between the two fault zones, we consider the Clackamas River fault zone to be potentially active. Geomatrix Consultants estimate a maximum surface rupture length of 22 km for the fault zone which corresponds with an MCE of Mw 6.6. 3.4.9 Grant Butte, Damascus, Tickle Creek Fault Zone Madin (1990) mapped an east - northeast - trending fault within the Portland Basin. A series of randomly oriented faults were mapped in an excavation within Troutdale Formation gravel on Grant Butte and comprise the informally -named Grant Butte fault (Geomatrix Consultants, 1995). The Damascus - Tickle Creek fault zone displaces Pliocene and possible Pleistocene sediments near Boring, Oregon ( Madin, 1990). The northwest - striking fault zone is defined by relatively short (less than 7 km) faults that comprise a zone approximately 17 km long. The combined fault zone is located approximately 32.4 km from the proposed pipeline corridor. The maximum estimated rupture length of 17 km reported by Madin (1990) can be used to calculate an MCE of Mw 6.5. 3.4.10 Other Fault Zones Several faults that are near the school site are discussed below. Based on either a lack of data indicating that these faults are active, or a preponderance of information suggesting that they are not active, we do not include them in the hazard analysis. 1 3.4.10.1 Sherwood Fault The proposed site lies approximately 3.8 km south of the school site. Geomatrix Consultants (1995) assessed the Sherwood fault for its seismogenic potential and concluded that there was no evidence for Quaternary activity. URS (2001) also performed a photogeologic study in this area, finding no evidence for recent movement. Based on the conclusions of Geomatrix Consultants (1995) and our photogeologic analysis, we do not consider the Sherwood fault to be potentially active. 1 3.4.10.2 Dairy Creek Fault The Dairy Creek fault is a relatively short structure that has been mapped on the basis of subsurface geophysical anomalies (Ian Madin, DOGAMI, personal communication, 2000). There UILS \Por6\projects25695391 TTSD Nberta Rider\ TTSD _seisrroc_hazard.doc\31- JUL -03 3-8 I SECTIONTHREE Seismic Conditions is no evidence for surface expression of the fault, and it does not appear to be structurally or kinematically associated with any nearby faults, and it has not been associated with historic seismicity. Based on a lack of information suggesting that the fault is potentially active, we do not consider it in the hazard analysis. 3.4.10.3 Beaverton Fault The west - southwest - striking Beaverton fault is located to the north of the proposed school. The fault has been located on the basis of geophysical anomalies. No additional information regarding the activity or seismic potential of the fault is currently available, thus we did not consider it in the hazard analysis. 3.4.11 Cascadia Subduction Zone The megathrust and intraslab region in the subducting Juan de Fuca plate represent two very different seismic sources within the Cascadia subduction zone. Due to the duration and distance I effects on ground motion, the megathrust rupture will be considered in this hazard analysis. 3.4.11.1 Megathrust Paleoseismic evidence (e.g., Atwater et al., 1995) and historic tsunami studies (Satake et al., 1996) indicate that the most recent megathrust earthquake in 1700 probably ruptured the full length of the Cascadia subduction zone and was about M 9 in size. Thus, seismic hazard evaluations need to consider future earthquakes of this magnitude, although data cannot preclude the possibility that smaller events have occurred in the past along the megathrust. A significant factor that will control the ground- shaking hazards posed by the Cascadia subduction zone revolves around the location of the megathrust zone. The eastern edge of the megathrust is allowed to vary from about 25 miles offshore to beneath the Coast Ranges with a preferred location beneath the coastline. This results in a source -to -site distance of approximately 120 -km to the site. We adopt a range of maximum magnitudes from M 8 to 9 with the latter given the highest weight. I I I \\Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seisrnic_hazard.doc\31- JUL -03 3-9 I SECTIONFOUR Design Ground Motion 4.1 GROUND MOTION ANALYSES Several factors control the level and character of earthquake ground shaking. These factors are in general: (1) rupture dimensions, geometry, and orientation of the causative fault; (2) distance from the causative fault; (3) magnitude of the earthquake; (4) the rate of attenuation of the seismic waves along the propagation path from the source to site; and (5) site factors including the effects of near - surface geology particularly from soils and unconsolidated sediments. Other factors, which vary in their significance depending on specific conditions, include slip distribution along the fault, rupture process, footwall /hanging -wall effects, and the effects of crustal structure such as basin effects. In this section, probabilistic analyses have been reviewed to evaluate the ground shaking hazard at the site. This data is being reviewed because insufficient knowledge exists regarding seismic sources in the site region to reliably estimate ground motions associated with the MCE using deterministic methods. 4.1.1 Geomatrix 1995 Probabilistic Study The probabilistic seismic hazard analysis conducted for the 1995 Geomatrix Report produced maps for given design return periods for the State of Oregon. The peak horizontal acceleration experienced at the site for a "500- year" return period on bedrock is 0.19 g. 4.1.2 URS 2001 Probabilistic Study The probabilistic seismic hazard analysis conducted by URS in the Tualatin Valley (URS, 2001) produced peak ground accelerations anticipated for given design return periods for the State of Oregon. The peak horizontal acceleration experienced at the new school site for a "500- year" return period was selected to be similar to peak ground acceleration value calculated for a site with similar subsurface conditions in the 2001 study. This peak ground acceleration is anticipated to be 0.22 g. 4.1.3 URS /DOGAMI 2000 Portland Metropolitan Study The probabilistic seismic hazard analysis conducted by URS for the Oregon Department of Geology and Mineral Industries produced maps for given design return periods for the Portland Metropolitan Area (Wong et al, 2000). The peak horizontal acceleration experienced at the site for a "500- year" return period for bedrock is modeled to be 0.20 to 0.25 g. 4.1.4 1998 OSSC Zonation The site lies within Seismic Zone 3 as defined by the 1998 version of the Oregon Structural Specialty Code (OSSC). Based on the soils encountered during the exploration program, OSSC Soil Type S (very dense soil and soft rock) represents the closest approximation to the site conditions and is recommended for use in design. The seismic response coefficients that URS I \\Por6\projects125695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\3t- JUL -03 4 -1 I SECTIONFOUR Design Ground Motion Corresponds with Z = 0.3 and Sc are C = 0.33 and C = 0.45 and were obtained from tables 16 -Q and 16 -R of the UBC, respectively. 4.1.5 Results Comparison The probabilistic seismic hazard analyses reviewed above are compared in Table 1 below. TABLE 1: COMPARISON OF PEAK GROUND ACCELERATIONS 2001 IIRS' "500',' - OSSC 1998 "500" M ` � �Refe c ence 1995 Geomatrix °500 "ear event . ear event (C ear event 4 .. ) • 500 Year event Y (Wong.et al ;for Site S� z 3 g,. w ....... d 200). Peak Ground Acceleration 0.19g 0.22g 0.20 — 0.25g 0.33g (gravity) 1 4.2 RECOMMENDED DESIGN GROUND MOTIONS As indicated above in Table 1, the OSSC 1998 peak ground acceleration and associated spectrum generally encompass the spectral response of the school site for the "500- year" return period. It is URS opinion that application of the 1998 OSSC is conservative at this site, and would be appropriate. Should the project team express an interest in exploring the site - specific response spectrum for the site, URS should be contacted to conduct the analyses required to generate the spectrum in accordance with Section 1631.2.2 of the 1998 OSSC. Should this approach be taken, it may be possible to reduce the design base shear for structural members by up to 20% in accordance with Section 1631.5.4 of the 1998 OSSC. I I 1 \ \Por6\projects125695391 TTSD Nberta RideATTSD _seisrrnc_hazard.doc\31- JUL -03 4 -2 I SECTIONFIVE Closure 1 5.1 ANTICIPATED FOUNDATION DESIGN Based on the soil conditions present at the site, it is anticipated that conventional continuous or isolated shallow foundations will be used to support the proposed structure. Footings will likely be founded on shallow silts or on bedrock. Detailed discussion of foundation design, allowable bearing capacity, expected settlements, and construction considerations are included in the companion URS geotechnical report entitled "Foundation Investigation, Alberta Rider Elementary School, Tigard- Tualatin School District, Tigard, Oregon." This report was submitted to the Tigard- Tualatin School District in July 2003. 5.2 SEISMIC HAZARDS Seismic hazards for the purposes of this report include liquefaction, tsunami /seiche inundation, seismically- induced landslides, surface rupture and ground ampliflication. These are evaluated and discussed separately in the following sections. 5.2.1 Liquefaction Hazard Liquefaction is the drastic loss of soil strength that can accompany ground shaking during a moderate to strong seismic event. During ground shaking, cyclic earthquake loading on the soil increases pore water pressure to a point where the effective stress on the soil is zero or even negative, resulting in suspension of soil particles in the water. Loose, granular soils located below the water table are generally susceptible to liquefaction. It should be noted that soil liquefaction, in and of itself, does not pose a risk to buildings and infrastructure. It is the phenomena accompanying liquefaction that can severely damage structures situated in or on the soil. These phenomena include settlement, lateral spreading, flow failures, and bearing capacity failure, which are discussed in the following sections. Based on the clay soils and shallow bedrock present at the site, it is URS opinion that there is not a liquefaction hazard at this site. The site is not at risk for the liquefaction - related phenomena of seismically induced settlement, lateral spreading, or bearing capacity failure. 5.2.2 Tsunami /Seiche Hazard URS understands that this site is not located near any body of water that is susceptible to tsunami • or seiche. Therefore, it is URS opinion that tsunami or seiche hazard at this site does not exist. 5.2.3 Seismic Slope Stability Hazard Because of the gentle slopes, the soil conditions and shallow rock found at the site, it is URS opinion that seismic slope instability is not a hazard at this site. UltS I \ \Por6\projects\25695391 TTSD Alberta Rider` TTSD _seisrrric_hazard.doc\31- JUL -03 5 -1 1 • SECTIONFIVE Closure 5.2.4 Surface Rupture Hazard Review of available geologic mapping indicates that no known fault trace passes beneath the proposed facility. Therefore, it is URS opinion that hazards from ground rupture at this site does not exist. 5.2.5 Ground Shaking Amplification Hazard Because of the soil conditions and the shallow rock found at the site, it is URS opinion that there is low risk for ground shaking amplification at this site. 111 • 1 I 1 I 1 I I I • URS • \ \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seisrrdc_hazard.doc\31- JUL -03 5 -2 1 SECTIONSIX Closure • The analyses, conclusions and recommendations presented in this report are based on site conditions as they existed at the time of our field exploration and the state of practice at the time - of this report. This report was prepared for the exclusive use of the Tigard- Tualatin School District and its agents and consultants. • 1 I 1 1 1 1 • URS I 1 1 I \\Por6\projects125695391 TTSD Alberta Rider\ TTSD _seisrruc_hazard.doc\31- JUL -03 6 -1 1 SECTIONSEVEN References Atwater, B.F., Nelson, A.R., Clague, J.J., Carver, G.A., Yamaguchi, D.K., Bobrowsky, P.T., Bourgeois, J., Darienzo, M.E., Grant, W.C., Hemphill - Haley, E., Kelsey, H.M. Jacoby, G.C., Nishenko, S.P., Palmer, S.P., Peterson, C.D., and Reinhart, M.A., 1995, Summary of coastal geologic evidence for past great earthquakes at the Cascadia subduction zone: Earthquake • Spectra, v. 11, p. 1 -18. Beeson, M.H., Fecht, K.R., Reidel, S.P., and Tolan, T.L. (1985). Regional Correlations Within ' the Frenchman Springs Member of the Columbia River Basalt Group: New Insights Into the Middle Miocene Tectonics of Northwestern Oregon: Oregon Geology, v. 47, p. 87 -96. Beeson, M.H., Tolan, T.L., and Anderson, J.L., (1989) The Columbia River Basalt Group in Western Oregon; Geologic Structures and Other Factors that Controlled Flow Emplacement Patterns, Geological Society of America Special Paper 239, p. 223 -246. ' Blakely, R.J., Wells., R.E., Yelin, T.S., Madin, I.P., and Beeson, M.H. (1995). "Tectonic setting of the Portland- Vancouver area, Oregon And Washington: Constraints From Low- altitude Aeromagnetic Data," Geological Society of America Bulletin v. 107, p. 1051.1062 Bott, J.D.J. and Wong, I.G. (1993). "Historical Earthquakes in and Around Portland, Oregon," Oregon Geology, v. 55, p. 116 -122. Geomatrix Consultants, Inc., 1995, "Seismic Design Mapping State of Oregon: Final Report ", prepared for the Oregon Department of Transportation, Contract 11688: Hammond, P.E., Anderson, J.L., and Manning, K.J. (1980). "Guide to the Geology of the Upper Clackamas and North Santiam Rivers Area, Northern Oregon Cascade Range," in Oles, K.F., Johnson, J.G., Niem, A.R., and Niem, W.A. (eds.), Geologic Field Trips in Western Oregon and Southwestern Washington: Oregon Department of Geology and Mineral Industries Bulletin 101, p. 133 -167. Johnson, S. Y., Dadisman, S. V., Childs, J. R., and Stanley, W. D. (1999) "Active Tectonics of the Seattle Fault and Central Puget Sound, Washington — Implications for Earthquake Hazards," Geological Society of America Bulletin, v. 111, p. 1042 -1053. Kramer, S.L. (1996). Geotechnical Earthquake Engineering. Prentice Hall, Upper Saddle River, New Jersey. Liberty, L.M., Trehu, A.M., Dougherty, M.D., and Blakely, R.J. (1996). "High- Resolution Seismic - Reflection Imaging of the Mt. Angel /Gales Creek Fault System Beneath the Willamette Valley: EOS, Transactions of the American Geophysical Union, v. 77, p. 655. Ludwin, R.S., Weaver, C.S., and Crosson, R.S., 1991, Seismicity of Washington and Oregon, in Neotectonics of North America, D.B. Slemmons, E.R. Engdahl, M.D. Zoback, and D.D. Blackwell (eds.): Geological Society of America Decade Map, v. 1, p. 77 -98. Madin, I.P. (1990). Earthquake Hazard Geology Maps of the Portland Metropolitan Area, Oregon. Oregon Department of Geology and Mineral Industries (DOGAMI), Open -File ' Report 0 -90 -2. Malone, S.D. and Bor, S.S. (1979). "Attenuation Patterns in the Pacific Northwest Based on Intensity Data and the Location of the 1872 North Cascads Earthquake," Bulletin of the Seismological Society of America, v. 69, p. 531 -546. URS \Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 7 -1 SECTIONSEVEN References Ordonez- Comparini, Gustavo A., 2000, SHAKE2000, A Computer Program for the 1 -D Analysis of Geotechnical Earthquake Engineering Problems, Ameritech Engineering. Orr, E.L. ; Orr, W.N. and Baldwin, E.M., 1992, Geology of Oregon, Fourth Edition, 1 Kendall/Hunt Publishing Company, Dubuque, Iowa. Pezzopane, S.K., 1993, Active Faults and Earthquake Ground Motions in Oregon, Ph.D. Thesis, University of Oregon, 208 p. Pratt, T.L, Odum, J., Stephenson, W., Williams, R., Dadisman, S., Holmes, M., and Haug, B. (2001). High - resolution seismic images of the late Pleistocene unconformity, ancestral ' Columbia River and Holocene faulting beneath the Portland - Vancouver urban area, Oregon and Washington: Bulletin of the Seismological Society of America v. 91. Priest, G.R., Woller, N.M., Black, G.L., and Evans, S.H. (1983). Overview of the Geology of the ' Central Oregon Cascade Range, Chapter 2, in Priest, G.R., and Vogt, B.F. (eds.), Geology and Geothermal Resources of the Central Oregon Cascade Range: Oregon Department of ' Geology and Mineral Industries Special Paper 15, p. 3 -28. Satake, K., Shimazaki, K., Tsuji, Y., and Ueda, K., 1996, Time and size of a giant earthquake in Cascadia inferred from Japanese tsunami records of January 1700: Nature, v. 379, p. 246 - 249. Sherrod, D.R. and Conrey, R.M. (1988). "Geologic Setting of the Breitenbush- Austin Hot Springs Area, Cascade Range, North- Central Oregon," in Sherrod, D.R. (ed.), Geology and Geothermal Resources of the Breitenbush- Austin Hot Springs Area, Clackamas and Marion Counties, Oregon: Oregon Department of Geology and Mineral Industries Open -File Report 0 -88 -5, p. 1 -14. Stover, C.W., and Coffman, J.L. (1993). Seismicity of the United States, 1568 -1989 (Revised), U.S. Geological Survey Profressional Paper 1527, 415 p. ' Thomas, G C., Crosson, R.S., Carver, D.L., and Yelin, T.S. (1996). "The 25 March 1993 Scotts Mills, Oregon Earthquake and Aftershock Sequence: Spatial Distribution, Focal Mechanisms, and the Mount Angel Fault," Bulletin of the Seismological Society of America, v. 86, p. 925 -935. Thorsen, G.W. ed. (1986). The Puget Lowland Eqrthquakes of 1949 and 165, Washington ' Division of Geology and Earth Resources, Information Circular 81, 113p. Toppozada, T.R., Real, C.R., and Parke, D.L. (1981). Preparation of Isoseismal Maps and I Summaries of Reported Effects for Ppre -1900 California Earthquakes, California Division of Mines and Geology Open File Report 81 -11, 181 p. Unruh, J.R., Wong, I.G., Bott, J.D.J., Silva, W.J., and Lettis, W.R., 1994. Seismotectonic ' Evaluation: Scoggins Dam, Tualatin Project, Northwestern Oregon; William Lettis & Associates and Woodward -Clyde Federal Services, unpublished final report prepared for the U.S. Bureau of Reclamation, Denver, CO. URS (2001). Geological and Seismic Hazard Evaluation South Mist Feeder Extension Project Phases IV and V, prepared for Northwest Natural. URS \\Por6\projects\25695391 TTSD Alberta Rider\ TTSD _seismic_hazard.doc\31- JUL -03 7-2 1 SECTIONSEVEN References Wald, D.J., Quitoriano, V., Heaton, T.H., and Kanomori, H. (1999). "Relationships Between Peak Ground Acceleration, Peak Ground Velocity, and Modified Mercalli Intensity in California," Earthquake Spectra, v. 15, p. 557 -564. 1 Wells, D. and Coppersmith, K.J., 1994, New earthquake magnitude and fault rupture parameters, Correlations among earthquake magnitude, rupture length, and fault displacement: Bulletin of the Seismological Society of America, v. 84, p. 974 -1002. ' Wells, R.E., Weaver, C.S., and Blakely, R.J., 1998, Forearc migration in Cascadia and its neotectonic significance: Geology, v. 26, p. 759 -762. Wong, I.G., 1997, The historical earthquake record in the Pacific Northwest: Applications and implications to seismic hazard assessment, in Earthquakes -- Converging at Cascadia, Symposium Proceedings, M. Wang and K. Neuendorf (eds.), Association of Engineering Geologists Special Publication 10 and Oregon Department of Geology and Mineral Industries Special Paper 28, p. 19 -36. ' Wong, I.G. and Bott, J.D.J., 1995, A look back at Oregon's earthquake history, 1981 -1994: Oregon Geology, v.57, p. 125 -139. Wong, I.G. and Silva, W.J., 1998, Earthquake ground shaking hazards in the Portland and Seattle metropolitan areas, in Geotechnical Earthquake Engineering and Soil Dynamics III, P. Dakoulas, M. Yegian, and R.D. Holtz (eds.): American Society of Civil Engineers Geotechnical Special Publication No. 75, v. 1, p. 66 -78. ' Wong, I.G., Pezzopane, S.K., and Blakely, R. (1999). "A Characterization of Seismic Sources in • Western Washington and Northwestern Oregon," (abs.) Seismological Research Letters, v. I 70, p. 221. Wong, I., Silva, W., Bott, J., Wright, D., Thomas, P., Gregor, N., Li, S., Mabey, M., Sojourner, A., and Wang, Y. (2000). Earthquake Scenario and Probabilistic Ground Shaking Maps for the Portland, Oregon, Metropolitan Area, Oregon Department of Geology and Mineral Industries Interpretative Map Series IMS -16, scale 1:62,500, 11 sheets with 16 p. text. Yeats, R.S., Graven, K., Werner, C., Goldfinger, C., and Popowsky, T. (1991). Tectonics of the Willamette Valley, Oregon; U.S. Geological Survey Open -File Report, 91- 441 -P, 47 p. Yelin, T.S. and Patton, H.J., (1991). "Seismotectonics of the Portland, Oregon, Region," Bulletin of the Seismological Society of America, v. 81, p. 109 -130. URS 1 1 i \\Por6\projects\25695391 TTSD Alberta Rider\TTSD_seismic hazard.doc\31- JUL -03 7 -3 I • - ',1.-- - _ - _-- . c, n . ` • . l i r , - . - � • .. '' \ I 4 \ • i—__,I...(1'," _ _ r',✓i: ^, i A 29.3, . ,'' ' : -�* , 1 111-'1:1-71:6' .. 1 j 1 ?? - ^ n -tea .'.. 1 .;;;;;I? 1 • 7 $ y - � " • P • ', / ' �' S' . r 7 ---. -� -..--........._,--.• �. • ' .'• - ti _ ' Y,,•;� /i• . lq ,1: .. " . 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LEGEND •ec ::aces ca•:e :�_• -_ec �.-.. �.....,:_.. . - — -- :. ;,v:.•, \'''4> �( • c } - •VaficouveL : _ - c_•.cea e a :car: on cox ^nro•.v .; •co • - ._ • Sv arr.,. snc. ::¢:.c^ ., : - ce i =. ..,, a : e •,2 ., yam, __ , PORTLAND :. - _- _ `� .:BASIN • * o•t sncwlr, e v�cen.:- 'e a ..r_ . _ - . • +. .., , ----- - -,:a: sucs,�Face e.. JIDar•e .__ acc Fe:e su : �� y NX ga Tl1ALATIN. -wY _. - - • : off ... :;° = 1 ' ' / V • --�'•_ . G .:• . • /:•: Vi ` \.; _ •F _ _ SITE - —:� • xy a • .. -.. ..- _ .. ::- ,.. • - = , • •‘. . REFERENCE: UNRUH Er. AL, 1994 11 Y 1 n G • TECTONIC STRUCTURES OF THE TUALATIN BASIN TTSD Alberta Rider Elementary School 0 URS July 2003 Seismic Site Hazard Investigation 25695391 Tigard, Oregon FIGURE 3